Immunoglobulins are antibodies secreted by plasma and tissue cells that identify and neutralize antigens, which are substances identified as foreign by the immune system. A common type of antibody structure is tetrametric, having two relatively long polypeptide chains, heavy (H) chains and two shorter polypeptide chains, light (L) chains. The Y-shaped structure arms specifically bind antigens (antigen binding fragment, Fab), and tails structure (Fc) binds to receptors on cells. There are five chain classes of immunoglobulins that are identified by different protein structure: gamma (IgG), mu (IgM), epsilon (IgE), alpha (IgA), and delta (IgD).
Human immunoglobulin G, IgG, is the predominant immunoglobulin involved in secondary immune responses. IgG includes four subclasses (IgG1, IgG2, IgG3, IgG4) and although concentrations in serum vary among subjects, in general IgG1 is found in the highest concentration followed by IgG2, and then IgG3 and IgG4 which have about equivalent concentration in serum. The maturation of the subclasses occurs with T helper cell dependence and IgG2 seems to require more help and evolves as stimulation persists.
However the binding of immunoglobulin subtypes and subclasses to antigens and the correlation of amounts of these proteins to prognosis and diagnosis is not well known. There is a need for methods of obtaining a prognosis or a diagnosis in a transplant donor and recipient and recipient candidate, in an allergy patient and in an autoimmune disease patient, by analyzing amounts of immunoglobulin subclasses and subtypes and determining extents of positive and negative outcomes in transplant candidates and recipients, and in the autoimmune disease and allergy patients.